Multi-level dc-dc converter with galvanic isolation and adaptive conversion ratio

ABSTRACT

A multi-level DC-DC converter includes an input side to receive a DC power having an input voltage and current, an output side to provide power to a load at a desired output voltage and current, and a plurality of transformer-isolated DC-DC converters connected between the input and output sides, with the transformer-isolated DC-DC converters being connected in series on one side and connected in parallel on another side. Each of the transformer isolated DC-DC converters further includes a power transformer having a primary winding and a secondary winding, and a plurality of switching devices each selectively operable in one of an On state and an Off state. Operating the switching devices in a complementary On state and Off state alternately at a controlled switching frequency provides for engaging the transformer isolated DC-DC converter and operating the switching devices in a simultaneously On state bypasses the transformer isolated DC-DC converter.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of, and claims priority to,U.S. patent application Ser. No. 14/469,002, filed Aug. 26, 2014, thedisclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Embodiments of the invention relate generally to power converters and,more particularly, to a DC-DC power converter that provides galvanicisolation and an adaptive conversion ratio.

Switch mode DC-DC converters are widely used for converting a giveninput electrical power to a desired output electrical power, with suchDC-DC converters being able to function as boost-type converters(converting an input voltage to a higher output voltage), buck-typeconverters (converting an input voltage to a lower output voltage), orconverters capable of both boosting or bucking the voltage. In addition,they can be classified as unidirectional or bi-directional convertersbased on their ability to flow power. In switch mode DC-DC converters,the input power is provided from a source to the converter through inputterminals on an input side, converted by the converter into the desiredoutput power and then output through output terminals on an output sideprovided to a load. The converter comprises a switching arrangement andpower transformer for transferring the electrical power from the inputside to the output side and for modulating the input electrical powerbefore it is provided to the output terminals. The switches employed insuch switching arrangements are typically comprised of solid stateswitches, such as MOSFET transistors for example. The transformerprovides for galvanic isolation between the input and output and voltagestep-up or step-down.

Often in switch mode DC-DC converters, the switches are activated bymeans of a control circuit controlling the phase angle, frequency (i.e.,frequency modulation) and/or duty cycle of the switches in the switchingarrangements to assume an ON-state (switch closed) or an OFF-state(switch open) in order to regulate voltage and current. For example, inthe case of MOSFET switches, the control circuit is adapted to provide agate voltage to switch the source-drain conduction channel ON(conducting) or OFF (non-conducting) in a timed manner. A rectifyingdiode may also be implemented by a three-terminal device, such as aMOSFET, by operating the control circuit driving the three-terminaldevice in a synchronous rectification mode.

In order to implement DC-DC converters used in high power applications,cascaded DC-DC converters with multi-level scheme may be used.

While existing pulse width modulation, phase shift control or frequencymodulation control techniques that are employed for controllingswitching in a DC-DC converter are effective for purposes of regulatingvoltage and current to a desired level, such control techniques cansuffer from efficiency issues when they are used over a wide regulationrange. To alleviate this, cascaded DC-DC converters have been used inprior art with coarse regulation performed by bypassing or engagingselected number of converters with external switches, and fineregulation done through modulation changes in a narrow range. Theexternal switches result in increased size and cost, and also lead toadditional power losses due to conduction drops.

Therefore, it is desirable to provide DC-DC converters and associatedcontrol scheme for operating the converters that increases theefficiency of the converters. It is also desirable that the DC-DCconverters include a minimal number of switches therein necessary toregulate voltage and current, such that the number of switches isreduced and a compact DC-DC conversion system is provided.

BRIEF DESCRIPTION OF THE INVENTION

Embodiments of the invention provide a multi-level DC-DC converter (andmethod of manufacture thereof) that provides galvanic isolation and anadaptive conversion ratio.

In accordance with one aspect of the invention, a multi-level DC-DCconverter includes an input side to receive a DC power having an inputvoltage and current, an output side to provide power to a load at adesired output voltage and current, and a plurality oftransformer-isolated DC-DC converters connected between the input sideand the output side, with the plurality of transformer-isolated DC-DCconverters being connected in series on one side and connected inparallel on another side. The multi-level DC-DC converter also includesa controller in operable communication with each of the plurality oftranformer-isolated DC-DC converters to control operation thereof. Eachof the plurality of transformer isolated DC-DC converters furtherincludes a power transformer having a primary winding arranged in aninput side converter stage on the input side and a secondary windingarranged in an output side converter stage on the output side, and aplurality of switching devices each selectively operable via thecontroller in one of an On state and an Off state to control voltage andcurrent flow therethrough, wherein the plurality of switching devices isoperated at a substantially fixed frequency and duty ratio by thecontroller.

In accordance with another aspect of the invention, a multi-level DC-DCconverter includes an input side to receive a DC power having an inputvoltage and current, an output side to provide power to a load at adesired output voltage and current, and a plurality of transformerisolated DC-DC converters connected between the input side and theoutput side such that the plurality of transformer isolated DC-DCconverters are connected in series on one side and connected in parallelon the other side, each of the plurality of transformer isolated DC-DCconverters including a bridge circuit, an input capacitor arranged inparallel with the bridge circuit, and a power transformer comprising aprimary winding arranged on the input side and a secondary windingarranged on the output side, wherein the bridge circuit and the inputcapacitor selectively control voltage and current flow through therespective tranformer isolated DC-DC converter.

In accordance with yet another aspect of the invention, a method ofmanufacturing a multi-level DC-DC converter includes providing aplurality of transformer isolated DC-DC converters, with each of theplurality of transformer isolated DC-DC converters comprising a powertransformer comprising a primary winding arranged in an input sideconverter stage and a secondary winding arranged in an output sideconverter stage and a plurality of switching devices arranged in theinput side converter stage, with each of the plurality of switchingdevices being selectively operable in one of an On state and an Offstate to control voltage and current flow to the primary winding. Themethod also includes providing a controller that is in operablecommunication with each of the plurality of transformer isolated DC-DCconverters and the plurality of switching devices therein, with thecontroller being programmed to operate the plurality of switchingdevices in each respective transformer isolated DC-DC converter in oneof the On state and the Off state so as to selectively engage anddisengage the respective transformer isolated DC-DC converter.

Various other features and advantages will be made apparent from thefollowing detailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate embodiments presently contemplated for carryingout the invention.

In the drawings:

FIG. 1 is a schematic block diagram of a multi-level DC-DC powerconverter, according to an embodiment of the invention.

FIG. 2 is a schematic block diagram of a multi-level DC-DC powerconverter, according to another embodiment of the invention.

DETAILED DESCRIPTION

Embodiments of the invention provide a multi-level DC-DC power converterthat provides galvanic isolation and an adaptive conversion ratio. Anumber of transformer isolated DC-DC converters are connected in serieson one side of the power converter and connected in parallel on anotherside of the converter. Existing switches in each of the transformerisolated DC-DC converters are used to selectively engage and disengagethe respective converter, so as to provide for a multi-level DC-DC powerconverter having a variable conversion ratio.

Referring to FIG. 1, a multi-level DC-DC power converter 10 is shownaccording to one embodiment of the invention. The multi-level DC-DCpower converter 10 receives power from a power source 12, such as an ACinput power source, with the power from the AC power source 12 being fedto a rectifier bridge 14 such as the four diode rectifier shown inFIG. 1. The rectifier bridge 14 converts the AC power input to a DCpower such that a DC bus voltage and current is provided to an inputside 16 of the multi-level DC-DC power converter 10. Alternately, the DCpower to input side 16 can be supplied by a DC source or DC transmissionsystem.

Connected to an output side 18 of the multi-level DC-DC power converter10 is a load 20, with the load 20 receiving a power output from themulti-level DC-DC power converter 10 at a desired output voltage orcurrent. The load 20 may be in the form of a DC load that receives theoutput voltage and current directly from the multi-level DC-DC powerconverter 10, or the load 20 may be an AC load—such that an inverter(not shown) would receive the output voltage and current from themulti-level DC-DC power converter 10 and invert the DC power to an ACpower for use by the load 20.

As shown in FIG. 1, the multi-level DC-DC power converter 10 is composedof a plurality of transformer isolated DC-DC converters 22, 24, 26, 28(or “converter blocks”). While the multi-level DC-DC power converter 10is shown as having an arrangement of four transformer isolated DC-DCconverters 22, 24, 26, 28, it is recognized that a greater or lessernumber of DC-DC converters could be included. The transformer isolatedDC-DC converters 22, 24, 26, 28 are connected between the input side 16and the output side of the multi-level DC-DC power converter 10, withthe transformer isolated DC-DC converters 22, 24, 26, 28 being connectedin series on the input side 16 and connected in parallel on the outputside 18. The connection of the transformer isolated DC-DC converters 22,24, 26, 28 in series on the input side 16 and in parallel on the outputside 18 allows for the multi-level DC-DC power converter 10 to provide adesired conversion ratio between the input voltage and the outputvoltage via selective control of the individual DC-DC converters 22, 24,26, 28, as will be explained in greater detail below.

As shown in FIG. 1, each of the transformer isolated DC-DC converters22, 24, 26, 28 includes a power transformer 30 having a primary winding32 arranged in an input side converter stage 34 on the input side 16 anda secondary winding 36 arranged in an output side converter stage 38 onthe output side 18. A plurality of switching devices 40 thatcollectively control current through the primary winding 32 of the powertransformer 30 are also provided on the input side converter stage 34.According to an exemplary embodiment, the switching devices 40 areprovided as metal oxide semiconductor field effect transistors (MOSFETs)operable in an On state and an Off state to control current flowtherethrough. However, embodiments of the invention are not limited toMOSFETs. Any appropriate electronic switch can be used, such as, forexample, insulated gate bipolar transistors (IGBTs) in anti-parallelwith a diode, bipolar junction transistors (BJTs), and metal oxidesemiconductor controlled thyristors (MCTs). The switching devices (anddiodes) can be made with Silicon (Si), Silicon Carbide (SiC), GalliumNitride (GaN), or any suitable Wide Bandgap (WBG) material.

According to an exemplary embodiment, two switching devices 40 (e.g.,MOSFETs) are included in each transformer isolated DC-DC converter 22,24, 26, 28 and are arranged so as to provide a half-bridge circuittopology—indicated at 42. The half-bridge circuit topology 42 serves asa fundamental building block for each DC-DC power converter 22, 24, 26,28, with the switching devices 40 being controlled to provide a desiredpower conversion. It is recognized, however, that rather than twoswitching devices 40 being provided as a half-bridge circuit 42, thetransformer isolated DC-DC converters 22, 24, 26, 28 could instead eachinclude four switching devices 40 that are arranged so as to provide afull-bridge circuit topology 44, as is shown in FIG. 2.

As shown in FIG. 1, each of the transformer isolated DC-DC converters22, 24, 26, 28 also includes a pair of input capacitors 46 arranged inparallel with the switching devices 40 (i.e., with the half-bridgecircuit 42) that store and release DC power received on the input sideconverter stage 34 of the DC-DC converter. The controlling of theswitching devices 40 provides for the storing and releasing of DC powerby the input capacitors 46, with the DC power being selectively providedto the primary winding 32 of the power transformer 30.

Also included in the multi-level DC-DC power converter 10 is acontroller 50 that is in operable communication with the switchingdevices 40 in each transformer isolated DC-DC converter 22, 24, 26, 28.The controller 50 is programmed to selectively operate each of theplurality of switching devices 40 in an On state and Off state tocontrol current flow therethrough. In one embodiment, where theswitching devices 40 are MOSFETs, the controller 50 sends gating signalsto the MOSFETs to control the operation thereof in an On or Off state.In one embodiment, the controller 50 operates the switching devices 40in a complementary fashion at substantially square wave duty cycle tofeed the associated primary winding 32 with a substantially square wavevoltage from the associated DC input capacitors 46 when the respectiveDC-DC converter is engaged to flow power.

The controller 50 is programmed to implement a control scheme by whichboth the switching devices 40 are simultaneously kept ON to selectivelydisengage power flow through the associated DC-DC converter to theoutput 18. That is, the controller 50 is programmed to operate one ormore switching devices 40 in a transformer isolated DC-DC converter 22,24, 26, 28 in the On state so as to bypass the input capacitors 46, suchthat a respective transformer isolated DC-DC converter 22, 24, 26, 28can be disengaged. A respective transformer isolated DC-DC converter 22,24, 26, 28 can therefore be shorted on the input side 16 through theswitching devices 40 feeding the power transformer primary winding 32,thus causing the particular DC-DC converter 22, 24, 26, 28 to bebypassed. That is, the input capacitors 46 can be shorted by controllingthe switching devices 40—and with high frequency conversion, the inputcapacitors 46 can be small such that shorting them does not lead toexcessive losses. By selectively engaging and disengaging respectivetransformer isolated DC-DC converters 22, 24, 26, 28 in the multi-levelDC-DC power converter 10, an adaptive conversion ratio is achievable forthe multi-level DC-DC power converter, with a suitable conversion ratiobetween input and output voltage being selectable via the controlledoperation of each transformer isolated DC-DC converter 22, 24, 26, 28.

As a further means for disengaging a transformer isolated DC-DCconverter 22, 24, 26, 28, it is recognized that the output of aparticular DC-DC converter will be disengaged naturally if a dioderectifier 52 is used at the secondary winding 36 (as shown in FIG. 1) orif the gates of active switches (e.g., MOSFETS) (not shown) are turnedOFF at the secondary winding 36.

According to one embodiment, the controller 50—in being programmed toselectively cause one or more of the transformer isolated DC-DCconverters 22, 24, 26, 28 to be bypassed—first functions to determine adesired value of a voltage conversion ratio between the input voltageand the output voltage for the multi-level DC-DC power converter 10.This determination of the desired voltage conversion ratio may,according to one embodiment, be performed via an input to the controller50 from an operator and may be based on the ratings/requirements of thepower source 12 and the load 20 with which the multi-level DC-DC powerconverter 10 is connected. Based on the desired value of the voltageconversion ratio determined by the controller 50, the controller 50 thenfunctions to control operation of the switching devices 40 in eachrespective transformer isolated DC-DC converter 22, 24, 26, 28 toselectively engage/disengage each DC-DC converter and thereby controlthe conversion ratio of the multi-level DC-DC power converter 10.

According to an exemplary embodiment, the controller 50 may function tocontrol the switching devices 40 in each transformer isolated DC-DCconverter 22, 24, 26, 28 in a manner that causes the converters to beengaged at a peak of an AC cycle (as provided by power source 12).Beneficially, higher efficiency may be achieved by engaging thetransformer isolated DC-DC converters 22, 24, 26, 28 at the peak of anAC cycle.

Referring still to FIG. 1, it is shown therein that transformer isolatedDC-DC converter 28 further includes therein a chopper stage 54,according to an exemplary embodiment. The chopper stage 54 includes aswitching device 56 (e.g., MOSFET) and diode 58 positioned to receive aDC power from the rectifier circuit 14 and perform an initial conversionthereon, with the chopper stage 54 performing modulation to provide forthis conversion. The chopper stage 54 performs the initial conversionwith high efficiency, fast response and a smooth control, and thusallows for a “fine tuning” of the output voltage and/or current providedby the DC-DC converter 28. While only DC-DC converter 28 is shown inFIG. 1 as including a chopper stage 54 therein that provides for suchvoltage tuning, it is recognized that additional ones of the transformerisolated DC-DC converters 22, 24, 26 in multi-level DC-DC powerconverter 10 could also include such a chopper stage 54. In anotherembodiment, the voltage ratio “fine tuning” could be done throughmodulation of one or more of the DC-DC converters which are keptengaged, with “coarse tuning” done through selection of the number ofDC-DC converters which are engaged or disengaged.

Beneficially, embodiments of the invention thus provide a multi-levelDC-DC power converter that provides galvanic isolation and an adaptiveconversion ratio. Each of the transformer isolated DC-DC converters inthe multi-level DC-DC converter can be operated at a fixed frequency andduty ratio, therefore allowing high efficiency and optimized design andperformance in the multi-level DC-DC power converter. The efficiency canbe improved further by using resonant elements in the primary orsecondary side of the transformers 30 to reduce switching losses. Aparticular number of the DC-DC converters can be selectively engaged anddisengaged to select/provide a suitable conversion ratio between inputand output voltage.

Of further benefit, as the switching devices used within each of theDC-DC converters are used to provide for the engaging/disengaging of therespective converters, no additional switches are required, therebyproviding a high efficiency in the converter and providing a compactconverter at lower cost. Due to its reduced size, the compact DC-DCconverters are thus useable in applications such as laptop chargers orother portable equipment.

According to one embodiment of the invention, a multi-level DC-DCconverter includes an input side to receive a DC power having an inputvoltage and current, an output side to provide power to a load at adesired output voltage and current, and a plurality oftransformer-isolated DC-DC converters connected between the input sideand the output side, with the plurality of transformer-isolated DC-DCconverters being connected in series on one side and connected inparallel on another side. The multi-level DC-DC converter also includesa controller in operable communication with each of the plurality oftranformer-isolated DC-DC converters to control operation thereof. Eachof the plurality of transformer isolated DC-DC converters furtherincludes a power transformer having a primary winding arranged in aninput side converter stage on the input side and a secondary windingarranged in an output side converter stage on the output side, and aplurality of switching devices each selectively operable via thecontroller in one of an On state and an Off state to control voltage andcurrent flow therethrough, wherein the plurality of switching devices isoperated at a substantially fixed frequency and duty ratio by thecontroller.

According to another embodiment of the invention, a multi-level DC-DCconverter includes an input side to receive a DC power having an inputvoltage and current, an output side to provide power to a load at adesired output voltage and current, and a plurality of transformerisolated DC-DC converters connected between the input side and theoutput side such that the plurality of transformer isolated DC-DCconverters are connected in series on one side and connected in parallelon the other side, each of the plurality of transformer isolated DC-DCconverters including a bridge circuit, an input capacitor arranged inparallel with the bridge circuit, and a power transformer comprising aprimary winding arranged on the input side and a secondary windingarranged on the output side, wherein the bridge circuit and the inputcapacitor selectively control voltage and current flow through therespective tranformer isolated DC-DC converter.

According to yet another embodiment of the invention, a method ofmanufacturing a multi-level DC-DC converter includes providing aplurality of transformer isolated DC-DC converters, with each of theplurality of transformer isolated DC-DC converters comprising a powertransformer comprising a primary winding arranged in an input sideconverter stage and a secondary winding arranged in an output sideconverter stage and a plurality of switching devices arranged in theinput side converter stage, with each of the plurality of switchingdevices being selectively operable in one of an On state and an Offstate to control voltage and current flow to the primary winding. Themethod also includes providing a controller that is in operablecommunication with each of the plurality of transformer isolated DC-DCconverters and the plurality of switching devices therein, with thecontroller being programmed to operate the plurality of switchingdevices in each respective transformer isolated DC-DC converter in oneof the On state and the Off state so as to selectively engage anddisengage the respective transformer isolated DC-DC converter.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

What is claimed is:
 1. A multi-level DC-DC converter comprising: aninput side to receive a DC power having an input voltage and current; anouput side to provide power to a load at a desired output voltage andcurrent; a plurality of tranformer-isolated DC-DC converters connectedbetween the input side and the output side, with the plurality oftranformer-isolated DC-DC converters being connected in series on oneside and connected in parallel on another side; and a controller inoperable communication with each of the plurality of tranformer-isolatedDC-DC converters to control operation thereof; wherein each of theplurality of tranformer isolated DC-DC converters comprises: a powertransformer comprising a primary winding arranged in an input sideconverter stage on the input side and a secondary winding arranged in anoutput side converter stage on the output side; and a plurality ofswitching devices each selectively operable, via the controller, in oneof an On state and an Off state to control voltage and current flowtherethrough; wherein the plurality of switching devices is operated ata substantially fixed frequency and duty ratio by the controller.
 2. Themulti-level DC-DC converter of claim 1 further comprising a rectifiercircuit configured to rectify AC power from an AC power source to a DCpower, with the DC power being provided to the plurality of tranformerisolated DC-DC converters.
 3. The multi-level DC-DC converter of claim 1wherein the plurality of switching devices in each tranformer isolatedDC-DC converter comprises a half-bridge circuit.
 4. The multi-levelDC-DC converter of claim 1 wherein the plurality of switching devices ineach tranformer isolated DC-DC converter comprises a full-bridgecircuit.
 5. The multi-level DC-DC converter of claim 1 wherein each ofthe plurality of tranformer isolated DC-DC converters further comprisesone or more capacitors configured to store and release DC power receivedon the input side.
 6. The multi-level DC-DC converter of claim 5wherein, for each of the plurality of transformer isolated DC-DCconverters, the controller is programmed to operate a plurality ofswitching devices in the On state so as to bypass the respective inputcapacitors, such that a respective transformer isolated DC-DC convertercan be disengaged.
 7. The multi-level DC-DC converter of claim 6 whereinthe controller is programmed to selectively cause one or more of thetransformer isolated DC-DC converters to be bypassed, so as to control aconversion ratio of the multi-level DC-DC converter.
 8. The multi-levelDC-DC converter of claim 1 wherein, for each of the plurality oftransformer isolated DC-DC converters, the controller is programmed tooperate the plurality of switching devices in the On state and the Offstate alternately at the fixed switching frequency to engage thetranformer isolated DC-DC converter.
 9. The multi-level DC-DC converterof claim 1 wherein, for each of the plurality of transformer isolatedDC-DC converters, the controller is programmed to selectively operateeach of the plurality of switching devices in the On state and the Offstate such that the respective transformer isolated DC-DC converter isengaged at a peak of an AC cycle.
 10. The multi-level DC-DC converter ofclaim 1 wherein one or more of the plurality of tranformer isolatedDC-DC converters comprises a chopper stage to feed the input sideconverter stage of the respective tranformer isolated DC-DC converter,the chopper stage performing modulation to provide for regulation of thevoltage and/or current output from the respective tranformer isolatedDC-DC converter.
 11. The multi-level DC-DC converter of claim 1 whereinthe output side converter stage of each of the plurality of tranformerisolated DC-DC converters comprises one of a diode rectifier or anarrangment of active swithcing devices.
 12. A multi-level DC-DCconverter comprising: an input side to receive a DC power having aninput voltage and current; an ouput side to provide power to a load at adesired output voltage and current; a plurality of tranformer isolatedDC-DC converters connected between the input side and the output sidesuch that the plurality of tranformer isolated DC-DC converters areconnected in series on one side and connected in parallel on the otherside, each of the plurality of tranformer isolated DC-DC convertersincluding: a bridge circuit; an input capacitor arranged in parallelwith the bridge circuit; and a power transformer comprising a primarywinding arranged on the input side and a secondary winding arranged onthe output side; wherein the bridge circuit and the input capacitorselectively control voltage and current flow through the respectivetranformer isolated DC-DC converter.
 13. The multi-level DC-DC converterof claim 12 further comprising a controller in operable communicationwith each of the plurality of tranformer isolated DC-DC converters toselectively operate each respective bridge circuit, the controller beingprogrammed to: determine a desired value of a voltage conversion ratiobetween the input voltage and the output voltage; and control operationof the bridge circuit in each respective tranformer isolated DC-DCconverter based on the desired value of the voltage conversion ratio;wherein one or more of the tranformer isolated DC-DC converters may beshorted based on the controlled operation of the respective bridgecircuits, so as to bypass one or more of the tranformer isolated DC-DCconverters and set the voltage conversion ratio to the desired value.14. The multi-level DC-DC converter of claim 13 wherein, for each of theplurality of transformer isolated DC-DC converters, the controller isprogrammed to operate the bridge circuit so as to bypass the inputcapacitor, such that a respective transformer isolated DC-DC converteris bypassed.
 15. The multi-level DC-DC converter of claim 12 wherein oneor more of the plurality of tranformer isolated DC-DC converterscomprises a chopper stage to feed the input side converter stage of therespective tranformer isolated DC-DC converter, the chopper stageperforming modulation to provide for regulation of the voltage and/orcurrent output from the respective tranformer isolated DC-DC converter.16. The multi-level DC-DC converter of claim 12 wherein the bridgecircuit in each of the plurality of tranformer isolated DC-DC converterscomprises one of a half-bridge circuit and a full bridge circuit.
 17. Amethod of manufacturing a multi-level DC-DC converter, the methodcomprising: providing a plurality of tranformer isolated DC-DCconverters, each of the plurality of tranformer isolated DC-DCconverters comprising: a power transformer comprising a primary windingarranged in an input side converter stage and a secondary windingarranged in an output side converter stage; and a plurality of switchingdevices arranged in the input side converter stage, with each of theplurality of switching devices being selectively operable in one of anOn state and an Off state to control voltage and current flow to theprimary winding; and providing a controller that is in operablecommunication with each of the plurality of tranformer isolated DC-DCconverters and the plurality of switching devices therein, with thecontroller being programmed to operate the plurality of switchingdevices in each respective tranformer isolated DC-DC converter in one ofthe On state and the Off state so as to selectively engage and disengagethe respective tranformer isolated DC-DC converter.
 18. The method ofclaim 17 wherein each of the plurality of tranformer isolated DC-DCconverters further comprises one or more input capacitors that areselectively shorted based on the operation of the plurality of switchingdevices in one of the On state and the Off state, so as to so as toselectively engage and disengage the respective tranformer isolatedDC-DC converter.
 19. The method of claim 17 wherein one or more of theplurality of tranformer isolated DC-DC converters further comprises achopper stage that performs a modulation to provide for regulation of aninput voltage or current provided to a respective tranformer isolatedDC-DC converter.